The present invention relates to Vector Graphics Display Processors.
A Vector Graphics Display Processor is a special purpose computer which converts stored numerical information into a graphical display on a cathode ray tube (CRT). In general, the coordinates of the endpoints of the respective straight lines comprising an image are stored in coordinate memory within the Display Processor. The endpoint coordinates are typically X, Y coordinates for two dimensional images and X, Y, Z coordinates for three dimensional images. The coordinates are sequentially fetched from memory and passed to the Vector Graphics Display Processor, which includes a line generator device for generating respective voltage ramps from the previous X coordinate to the current X coordinate and from the previous to the current Y coordinate. Such ramps are applied as drive signals to the deflection amplifiers of a standard CRT. Thus, a complex image can be drawn from a series of short straight lines.
It should be noted that such a Vector Display Processor develops the image by moving the electron beam within the CRT only to those places on the screen where a line is being generated. This is to be distinguished from a raster scan image in which the entire CRT screen is scanned by the electron beam in a regular pattern regardless of what information is being displayed.
When the electron beam strikes the face of the CRT, the point of impingement is illuminated for a few milliseconds. To ensure that a continuous image is perceived on the screen by an observer, the electron beam must retrace or refresh the entire image on the order of 35 times per second. If the entire image is drawn less frequently, the image will appear to flicker. If the image is moved slightly each time it is redrawn, a smooth movement of the image will be perceived by the observer. Accordingly, special purpose computing hardware is typically included in the display processor, interposed between the coordinate memory and the line generator to selectively modify the coordinate values fetched from memory prior to application to the line generator. In this manner, a dynamic image can be presented to the observer. The special purpose computing hardware typically performs a mathematical transformation such as rotation, translation, and scaling of an image.
In general, dynamic refreshed Vector Graphics Display Processors in the form of peripheral devices adapted for cooperation with a general purpose (host) computer are known. Examples of devices for vector generation are described in U.S. Pat. Nos. 3,482,086 issued on Dec. 2, 1969 to C. F. Caswell; 3,638,214 issued to Scott et al. on June 25, 1972; 3,746,912 issued to Redecker et al. on July 17, 1983; 3,772,563 issued to R. D. Hasenbalg on Nov. 13, 1973; 3,869,085 issued to P. F. Green on Mar. 4, 1975; 3,996,673 issued to C. J. Vorst et al. on Dec. 14, 1976; 4,027,148 issued to R. D. Rosenthal on May 31, 1977; 4,074,359 issued to R. D. Hazenbalg on Feb. 14, 1978; and 4,365,305 issued to J. P. MacDonald et al. on Dec. 21, 1982. Special purpose hardware for performing the mathematic translations on the data prior to line generation is also known. An example is described in U.S. Pat. No. 3,763,365 issued Oct. 2, 1973 to C. L. Seitz. Such vector graphics display units, however, tend to be relatively expensive.
Low cost hardwired special purpose graphics processors have been developed for particular applications, such as, for example, the field of neuroscience. Description of special purpose hardwired Graphics Display Processors as used in neuroscience are described in the following articles, which are incorporated herein by reference: Capowski, "Characteristics of a Neuroscience Computer's Graphics Displays and a Proposed System to Generate Those Displays", Computer Graphics 10: 2, 1976, pp. 257-261; Capowski, "The Neuroscience Display Processor", Computer 11: 11, 1978 pp. 48-58; Capowski, "The Neuroscience Display Processor Model 2", Proceedings of the Digital Equipment Users Society, 5: 2, 1978 pp. 763-767; Capowski and Sedivec, "Accurate Computer Reconstruction and Graphics Display of Complex Neurons Using State of The Art Interactive Techniques", Comp. Biomed Res 14: 518-532, 1981; and McInroy and Capowski, "A Graphic Subroutine Package For The Neuroscience Display Processor", Computer Graphics 11: 1, 1977, pp. 1-12.
Such special applications vector graphics display processors, however, tend to be relatively complex, slow, and require a relatively complex and costly host computer.